Carbocyanine dyes



Patented Sept. 2, 1952 [2,609,371 CARBOCYANINE YEs- John Charles Firestine, South River, N. J., as-

signor to E. I. du Pont de Ncmours & Company, Wilmington, Del.,ja'. 'corporation of Delaware No Drawing. Application DecemberZG, 1949,

Serial No. 134,146

Claims.

This invention relates to 5-carboxybenzoxazole carbocyanine dyes and to their preparation and use. More particularly it relates to 5-carboxybenzoxazole carbocyanine dyes which has a hydrocarbon group substituted on the central carbon atom of the trimethine chain. The iri- 'vention also relates to intermediates for the preparation of such cyanine dyesand to photo'- graphic silver halide emulsions containing the dyes in sensitizing amounts.

An object of this invention is to provide a new class of benzoxazole carbocyanine dyes. A

further object is to provide such dyes which have good sensitizing properties for silverhalidejemulsions. A still further objectis to provide such dyes which do not leave an objectionable residual stain when the dyes are used inphotographic silver halide emulsions. Another object of the invention is to provide'newand useful colloid silver halide emulsions sensitized with the aforesaid dyes. Yet another object is to provide a prac'ticalfmethod for preparing the aforesaid dyes and intermediates therefor. Still other objects will be apparent from the following description of the invention.

It has been found that benzoxazole carbocyanine dyes which contain a carboxylic acid substituent in the 5-position of each benzene nucleus and ahydrocarbon substituent on the central carbon atom of thetrimethine chain are unique cyanine dyes in that they are good sensitizing agents for increasing the optical sensitivity of colloid silver halide emulsions. The 6,6-'-carboxybenzthiazole carbocyanine ethiodide on the other;

hand desensitizes a gelatino silver bromochloride emulsion. The 5-carboxy dyes of this invention, moreover, do not leave an objectionable residual stain in photographiclayers after the development and fixing, etc., of the exposed photographic elementhas been completed. The good sensitizing properties of the carbocyanine dyesof this invention are somewhat surprisingwhere R is an alkyl radical of 1 to 12 carbon atoms or is a benzyl radical, R1 is a hydrocarbon radical, e. g., methyl, ethyl, propyl, isopropyl, hexyl, dodecyl, phenyl, naphthyl, and benzyl and X is the negative radical of an acid, e. g., halogen suchasCl, Br and I: perchlorate, SCN, p-toluene sulfonate, methylsulfate ethyl sulfate-, etc.

The dyes of forumla (I) can be made from- 2 methyl- 5- carboxybenzoxazole by converting this base into a cycloammonium salt with -a quaterniz'ing or salt-forming agent such as an alkyl salt or ester of an alcohol radical witha suitable acid; e. g., an alkyl halide, alky1 nitrate, alkylper'chlorate, alkyl-p-toluene sulfonate, alkyl sulfamate, benzyl halide, alkyl "sulfate, etc. The cycloammonium salts of 2-methyl-5-carboxybenzo'xazole may be represented by the general formula:

.0 c-cm Hooc- X/ \R v where R has the same significance in formula (I).

The cycloammonium salts of formula (II) may be converted into carbocyanine dyes of formula (I) by reacting them with an orthoester of a carboxylic acid, e. g., methyl and ethyl orthoacetate, orthopropionate, orthobenzoate, etc.

When an orthoester of a saturated aliphatic mono-carboxylic acid is used, R1 is an alkyl and when an orthoester of an aromatic carboxylic acid is used R1 is'a'n aryl radical,'etc.

' The salt-forming reaction and cyanine dye condensation reaction may be carried out simultaneously if desired by admixing 2-methyl-5- carboxybenzoxazole in any suitable manner with the alkyl or aralkyl salt and the orthoester of the aliphatic or aromatic carboxylic acid.

The carbocyaninedyes of formula (I) are useful photographic sensitizing dyes and maybe incorporated with colloid-silver halide emulsions of various types including silver chloride, silver bromide, silver chlorobromide, silver iodobromide, simpleand mixed emulsions. Various types of colloids canbe used as binding agents for the light-sensitive silver halide grains, e. g., gelatin, albumin, agar agar;-hydrophilic cellulose acetate,

polyamides, hydrolyzed ethylene/vinyl acetate copolyme'rs polyvinyl alcohol, etc.

The new carbocyanine dyes can be added to emulsions in variousways. Thus, theymay be added in the form of solutions. Suitable solvents are the water-miscible alcohols, e. g., methyl and ethyl alcohol, whichuma'y be substantially anhydrous or diluted with water. Dyes can be added to emulsion duringv any desired stage of its production-in the conventional manners. However,

' theyare preferably added tothe finished emul- 2-MethyI-S-carboxybenzoxazole To ,100 grams (0.653 mol). of 3-amino-4-hydroxybenzoic acid, there was; carefully added 150 grams (1.47 mols) of acetic anhydride. -The mixture was refluxed gently for minutes. During the operation a solid crystallized out of the mixture at first, and then gradually went back into solution as heating continued. Acetic acid and acetic anhydride were distilled ofi slowly at atmospheric pressure. The distilled acetic acid-acetic anhydride mixture was poured back into the distilling flask, and the mixture was subjected to redistillation. This stepwas taken to insure completion of the ring closure. Finally the above oxazole compound was distilled having a boiling point of 230-250 C. at 2 mm. The crude material weighed 80 grams and was recrystallized from alcohol, yielding 63 grams of white solid having a melting point of 188-189 C. and the above structural formula. A second crop was obtained amounting to 14 grams. The combined material represented 44% theoretical.

' The invention will be further illustrated but is not intended to be limited by the'following examples. V

' Example I Preparation of a dye having the formula E H000 CH3 00011 I CQH; I Ce s In a suitable Erlenmeyer flask were placed 8.85 grams (0.05 mol) of Z-methyI-B-carboxybenzoxazole and 7.7 grams (0.05 mol) of diethyl sulfate. The mixture was heated over a flame until it was just melted, and then was held at 140 in an oil bath for two hours. At that time 40 milliliters of dry pyridine and 15 milliliters of ethyl orthoacetate were added. The resulting mixture was refluxed for .10 minutes, a deep orange color formed and the mixture was cooled and diluted to a volume of 1000'milliliters of ether, and allowed to stand. The dye'separated as an oil- The ether solution was decanted from the oily dye. One liter of approximately 2% aqueous KIsolution was addedto the'oil and a non-dye residue which formed was filtered off. The filtrate was acidified with 20 milliliters of glacial acetic acid and an orange dye separated. It was filtered, washed with water and recrystallized from alcohol. A yield of 0.8- gram of orange dye was obtained which melted at 248 C.-251 C. This dye had its absorption maximum at 4920 A in an ethanol solution. It is useful for sensitizing colloid silver halide emulsion layers, e. g., those of the type described in Example II.

Example II 02115 I C 7H5 A' mixture of 5.31 grams of 2-methyl-5-carboxybenzoxazole and 4.16 grams of diethyl sulfate were melted together and heated for four hours. at -130 C. Sixty milliliters of 'dry pyridine, 12 milliliters of ethyl orthoproprionate and six milliliters of propionic anhydride were then added and the mixture refluxed for 20 minutes. A deep orange color formed and after cooling and adding ether the dye separated as an oil. The oil was treated with KI solution and the crude iodide saltof-the dye separated out as a solid. The dye was dissolved in acetone'and precipitated with ether. This operation was re-,

peated and then the resulting dye was'recrystallized twice from alcohol. A yield of 0.22 gram melting at 233f235 C. of the dye having the above structural formula was obtained.

When this dye was added to a lithographic gelatino silver chromobromide emulsion it extended the sensitivity to 5600 A with a peak at Example Hi The dyes of Examples I and II can be converted into the --SCN salt by adding a water solution of KSCN or NaSCN to the ethsulfate oil of Examples I and II, separating the precipitated dye and recrystallizing it from ethanol solution.

Various other carbocyanine dyes containing different alkyl salt radicals than thosedescribed in the foregoing examples can be made in a similar manner by substituting for the diethyl sulfate other alkyl salts such as ethyl p-toluene sulfonate, methyl p-toluene sulfonate, methyl perchlorate, ethyl iodide, methyl chloride, ethyl benzenesulfonate.

The ethylethosulfate salts of the foregoing examples can be converted into other salts by ametathetical reaction, e. g., into the corresponding bromideor iodide by the addition of sodium iodide, potassium bromide, ammonium chloride, potassium thiocyanate, etc.

Similarly in place of the ethyl orthopropionate of the above examples, there may be substituted other alkyl orthoesters of aliphatic'monocarboxylicacids, e. g., methyl orthoacetate, ethyl orthoacetate, ethyl ortho a. thiophene carboxylate, ethyl orthobutyrate, methyl orthovalerate, orthocapr'oate, diethyl methylorthocaproate, ethyl ortho-'yphenoxy-butyrate, methyl orthophenylacetate, ethyl ortho-para-toluate, ethyl di-npropyl orthopropionate.

The dyes of this invention, as stated above, have the advantage that they do not leave an objectionable residual stain after the exposure, development and fixing of a photographic element bearing one or more colloid silver halide 'HOOC emulsion layers containing one or more of such dyes has been completed. Another advantage resides in the fact that the dyes have increased solubility in solvents and can be readily introduced into emulsions. Still other advantages will wherein R is a hydrocarbon radical taken from the group consisting of alkyl and benzyl, R1 is a hydrocarbon radical and X is a negative radical of an acid.

2. A carbocyanine dye of the formula:

CzHs I COOH 3. A carbocyanine dye having the formula:

(132m c OH CzHs SCN (32: 5

4. A carbocyanine dye of the formula:

OOH=CCH= HOOG- N/ 0.419. (1.11. 5. The carbocyanine dye of the formula:

- CzHs OOOH COOH

S ON hHs JOHN CHARLES FIRESTINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,166,736 White et a1. July 18, 1939 2,263,749 White et a1 Nov. 25, 1941 2,322,015 Hamer et a1. June 15, 1943' 2,340,882 Kendall Feb. 8,1944 2,342,546 Kendall Feb. 22, 1944 2,353,164 Kendall et a1 -July 11, 1944 OTHER REFERENCES Chem. Abstracts 16 :3101 (Ab. of Br. Med. Journal, 1922 I 514-515).

Chem. Abstracts 19:530 (Ab. of Proc. Roy Soc., London, 963 317-333, 1924). 

1. THE CARBOCYANINE DYES OF THE FORMULA: 